Hydrazone-based charge transport materials

ABSTRACT

Improved organophotoreceptor comprises an electrically conductive substrate and a photoconductive element on the electrically conductive substrate, the photoconductive element comprising:
         (a) a charge transport material having the formula       

     
       
         
         
             
             
         
       
         
         
           
              where R 1  and R 2  are, each independently, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; 
             R 3  and R 4  are, each independently, H, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; 
             X 1  and X 2  are, each independently, a linking group; 
             Y 1  and Y 2 , each independently, comprise an arylamine group; and 
             Z is a bridging group; and 
             (b) a charge generating compound. 
             Corresponding electrophotographic apparatuses and imaging methods are described.

FIELD OF THE INVENTION

This invention relates to organophotoreceptors suitable for use inelectrophotography and, more specifically, to organophotoreceptorsincluding a hydrazone-based charge transport material having twoarylamine hydrazone groups bonded together through bridging and linkinggroups.

BACKGROUND OF THE INVENTION

In electrophotography, an organophotoreceptor in the form of a plate,disk, sheet, belt, drum or the like having an electrically insulatingphotoconductive element on an electrically conductive substrate isimaged by first uniformly electrostatically charging the surface of thephotoconductive layer, and then exposing the charged surface to apattern of light. The light exposure selectively dissipates the chargein the illuminated areas where light strikes the surface, therebyforming a pattern of charged and uncharged areas, referred to as alatent image. A liquid or solid toner is then provided in the vicinityof the latent image, and toner droplets or particles deposit in thevicinity of either the charged or uncharged areas to create a tonedimage on the surface of the photoconductive layer. The resulting tonedimage can be transferred to a suitable ultimate or intermediatereceiving surface, such as paper, or the photoconductive layer canoperate as an ultimate receptor for the image. The imaging process canbe repeated many times to complete a single image, for example, byoverlaying images of distinct color components or effect shadow images,such as overlaying images of distinct colors to form a full color finalimage, and/or to reproduce additional images.

Both single layer and multilayer photoconductive elements have beenused. In single layer embodiments, a charge transport material andcharge generating material are combined with a polymeric binder and thendeposited on the electrically conductive substrate. In multilayerembodiments, the charge transport material and charge generatingmaterial are present in the element in separate layers, each of whichcan optionally be combined with a polymeric binder, deposited on theelectrically conductive substrate. Two arrangements are possible for atwo-layer photoconductive element. In one two-layer arrangement (the“dual layer” arrangement), the charge-generating layer is deposited onthe electrically conductive substrate and the charge transport layer isdeposited on top of the charge generating layer. In an alternatetwo-layer arrangement (the “inverted dual layer” arrangement), the orderof the charge transport layer and charge generating layer is reversed.

In both the single and multilayer photoconductive elements, the purposeof the charge generating material is to generate charge carriers (i.e.,holes and/or electrons) upon exposure to light. The purpose of thecharge transport material is to accept at least one type of these chargecarriers and transport them through the charge transport layer in orderto facilitate discharge of a surface charge on the photoconductiveelement. The charge transport material can be a charge transportcompound, an electron transport compound, or a combination of both. Whena charge transport compound is used, the charge transport compoundaccepts the hole carriers and transports them through the layer with thecharge transport compound. When an electron transport compound is used,the electron transport compound accepts the electron carriers andtransports them through the layer with the electron transport compound.

SUMMARY OF THE INVENTION

This invention provides organophotoreceptors having good electrostaticproperties such as high V_(acc) and low V_(dis).

In a first aspect, an organophotoreceptor comprises an electricallyconductive substrate and a photoconductive element on the electricallyconductive substrate, the photoconductive element comprising:

(a) a charge transport material having the formula:

where R₁ and R₂ are, each independently, an alkyl group, an alkenylgroup, an alkynyl group, an aromatic group, or a heterocyclic group;

R₃ and R₄ are, each independently, H, an alkyl group, an alkenyl group,an alkynyl group, an aromatic group, or a heterocyclic group;

X₁ and X₂ are, each independently, a linking group, such as a—(CH₂)_(m)— group, where m is an integer between 1 and 20, inclusive,and one or more of the methylene groups is optionally replaced by O, S,N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, anNR_(a) group, a CR_(b) group, a CR_(c)R_(d) group, or a SiR_(e)R_(f)where R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) are, eachindependently, a bond, H, a hydroxyl group, a thiol group, a carboxylgroup, an amino group, an alkyl group, an alkoxy group, an alkenylgroup, an alkynyl group, a heterocyclic group, an aromatic group, or apart of a ring group, such as cycloalkyl groups, heterocyclic groups, ora benzo group;

Y₁ and Y₂, each independently, comprise an arylamine group, such as acarbazole group, a julolidine group, and an (N,N-disubstituted)arylaminegroup; and

Z is a bridging group having the formula -Q₁-X₃-Q₂- where Q₁ and Q₂comprise, each independently, O, S, or NR where R is H, an alkyl group,an alkenyl group, an alkynyl group, a heterocyclic group, or an aromaticgroup; and X₃ comprises a —(CH₂)_(p)— group where p is an integerbetween 1 and 20, inclusive, and at least one of the methylene groups isreplaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h)group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i),R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxylgroup, a thiol group, a carboxyl group, an amino group, an alkyl group,an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclicgroup, an aromatic group, or a part of a ring group; and

(b) a charge generating compound.

The organophotoreceptor may be provided, for example, in the form of aplate, a flexible belt, a flexible disk, a sheet, a rigid drum, or asheet around a rigid or compliant drum. In one embodiment, theorganophotoreceptor includes: (a) a photoconductive element comprisingthe charge transport material, the charge generating compound, a secondcharge transport material, and a polymeric binder; and (b) theelectrically conductive substrate.

In a second aspect, the invention features an electrophotographicimaging apparatus that comprises (a) a light imaging component; and (b)the above-described organophotoreceptor oriented to receive light fromthe light imaging component. The apparatus can further comprise a tonerdispenser, such as a liquid toner dispenser. The method ofelectrophotographic imaging with photoreceptors containing the abovenoted charge transport materials is also described.

In a third aspect, the invention features an electrophotographic imagingprocess that includes (a) applying an electrical charge to a surface ofthe above-described organophotoreceptor; (b) imagewise exposing thesurface of the organophotoreceptor to radiation to dissipate charge inselected areas and thereby form a pattern of at least relatively chargedand uncharged areas on the surface; (c) contacting the surface with atoner, such as a liquid toner that includes a dispersion of colorantparticles in an organic liquid, to create a toned image; and (d)transferring the toned image to a substrate.

In a fourth aspect, the invention features a charge transport materialhaving Formula (I) above.

The invention provides suitable charge transport materials fororganophotoreceptors featuring a combination of good mechanical andelectrostatic properties. These photoreceptors can be used successfullywith toners, such as liquid toners, to produce high quality images. Thehigh quality of the imaging system can be maintained after repeatedcycling.

Other features and advantages of the invention will be apparent from thefollowing description of the particular embodiments thereof, and fromthe claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An organophotoreceptor as described herein has an electricallyconductive substrate and a photoconductive element including a chargegenerating compound and a charge transport material having two arylaminehydrazone groups bonded together through bridging and linking groups.These charge transport materials have desirable properties as evidencedby their performance in organophotoreceptors for electrophotography. Inparticular, the charge transport materials of this invention have highcharge carrier mobilities and good compatibility with various bindermaterials, and possess excellent electrophotographic properties. Theorganophotoreceptors according to this invention generally have a highphotosensitivity, a low residual potential, and a high stability withrespect to cycle testing, crystallization, and organophotoreceptorbending and stretching. The organophotoreceptors are particularly usefulin laser printers and the like as well as fax machines, photocopiers,scanners and other electronic devices based on electrophotography. Theuse of these charge transport materials is described in more detailbelow in the context of laser printer use, although their application inother devices operating by electrophotography can be generalized fromthe discussion below.

To produce high quality images, particularly after multiple cycles, itis desirable for the charge transport materials to form a homogeneoussolution with the polymeric binder and remain approximatelyhomogeneously distributed through the organophotoreceptor materialduring the cycling of the material. In addition, it is desirable toincrease the amount of charge that the charge transport material canaccept (indicated by a parameter known as the acceptance voltage or“V_(acc)”), and to reduce retention of that charge upon discharge(indicated by a parameter known as the discharge voltage or “V_(dis)”).

The charge transport materials can be classified as a charge transportcompound or an electron transport compound. There are many chargetransport compounds and electron transport compounds known in the artfor electrophotography. Non-limiting examples of charge transportcompounds include, for example, pyrazoline derivatives, fluorenederivatives, oxadiazole derivatives, stilbene derivatives, enaminederivatives, enamine stilbene derivatives, hydrazone derivatives,carbazole hydrazone derivatives, (N,N-disubstituted)arylamines such astriaryl amines, polyvinyl carbazole, polyvinyl pyrene,polyacenaphthylene, and the charge transport compounds described in U.S.Pat. Nos. 6,689,523, 6,670,085, and 6,696,209, and U.S. patentapplication Ser. Nos. 10/431,135, now U.S. Pat. No. 6,899,984;10/431,138, now U.S. Pat. No. 6,964,833; 10/699,364, now U.S. PublishedApplication No. 2005/0095519A1; 10/663,278, now U.S. Pat. No. 7,074,532;10/699,581, now U.S. Published Application No. 2005/0095518A1;10/449,554, now U.S. Pat. No. 6,749,978; 10/748,496, now U.S. Pat. No.6,887,634; 10/789,094, now U.S. Published Application No.2004/0241563A1; 10/644,547, now U.S. Pat. No. 6,991,882; 10/749,174, nowU.S. Published Application No. 2004/0152002A1; 10/749,171, now U.S.Published Application No. 2004/0170910A1; 10/749,418, now U.S. Pat. No.7,118,840; 10/699,039, now U.S. Pat. No. 7,008,743; 10/695,581, U.S.Pat. No. 7,083,884; 10/692,389, now U.S. Pat. No. 6,960,418; 10/634,164,now U.S. Pat. No. 7,029,812; 10/663,970, now U.S. Pat. No. 6,768,010;10/749,164, now U.S. Published Application No. 2004/0157145A1;10/772,068, now U.S. Pat. No. 7,090,953; 10/749,178, U.S. Pat. No.7,014,968; 10/758,869, now U.S. Published Application No.2005/0158642A1; 10/695,044, now U.S. Published Application No.2005/0089783A1; 10/772,069, now U.S. Published Application No.2004/0191655A1; 10/789,184, U.S. Pat. No. 7,011,918; 10/789,077, U.S.Pat. No. 7,108,948; 10/775,429, now U.S. Published Application No.2004/0219446A1; 10/670,483,U.S. Pat. No. 7,037,632; 10/671,255, now U.S.Pat. No. 7,011,917; 10/663,971, now U.S. Published Application No.2005/0058920A1; 10/760,039, now U.S. Pat. No. 7,115,347. All the abovepatents and patent applications are incorporated herein by reference.

Non-limiting examples of electron transport compounds include, forexample, bromoaniline, tetracyanoethylene, tetracyanoquinodimethane,2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone,2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone,2,6,8-trinitro-indeno[1,2-b]thiophene-4-one, and 1,3,7-trinitrodibenzothiophene-5,5-dioxide, (2,3-diphenyl-1-indenylidene)malononitrile,4H-thiopyran-1,1-dioxide and its derivatives such as4-dicyanomethylene-2,6-diphenyl-4H-thiopyran-1,1-dioxide,4-dicyanomethylene-2,6-di-m-tolyl-4H-thiopyran-1,1-dioxide, andunsymmetrically substituted 2,6-diaryl-4H-thiopyran-1,1-dioxide such as4H-1,1-dioxo-2-(p-isopropylphenyl)-6-phenyl-4-(dicyanomethylidene)thiopyranand4H-1,1-dioxo-2-(p-isopropylphenyl)-6-(2-thienyl)-4-(dicyanomethylidene)thiopyran,derivatives of phospha-2,5-cyclohexadiene,alkoxycarbonyl-9-fluorenylidene)malononitrile derivatives such as(4-n-butoxycarbonyl-9-fluorenylidene)malononitrile,(4-phenethoxycarbonyl-9-fluorenylidene)malononitrile,(4-carbitoxy-9-fluorenylidene)malononitrile, anddiethyl(4-n-butoxycarbonyl-2,7-dinitro-9-fluorenylidene)malonate,anthraquinodimethane derivatives such as11,11,12,12-tetracyano-2-alkylanthraquinodimethane and11,11-dicyano-12,12-bis(ethoxycarbonyl)anthraquinodimethane, anthronederivatives such as 1-chloro-10-[bis(ethoxycarbonyl)methylene]anthrone,1,8-dichloro-110-[bis(ethoxy carbonyl)methylene]anthrone,1,8-dihydroxy-10-[bis(ethoxycarbonyl)methylene]anthrone, and1-cyano-10-[bis(ethoxycarbonyl)methylene)anthrone,7-nitro-2-aza-9-fluroenylidene-malononitrile, diphenoquinonederivatives, benzoquinone derivatives, naphtoquinone derivatives,quinine derivatives, tetracyanoethylenecyanoethylene, 2,4,8-trinitrothioxantone, dinitrobenzene derivatives, dinitroanthracene derivatives,dinitroacridine derivatives, nitroanthraquinone derivatives,dinitroanthraquinone derivatives, succinic anhydride, maleic anhydride,dibromo maleic anhydride, pyrene derivatives, carbazole derivatives,hydrazone derivatives, N,N-dialkylaniline derivatives, diphenylaminederivatives, triphenylamine derivatives, triphenylmethane derivatives,tetracyano quinodimethane, 2,4,5,7-tetranitro-9-fluorenone,2,4,7-trinitro-9-dicyanomethylene fluorenone, 2,4,5,7-tetranitroxanthonederivatives, 2,4,8-trinitrothioxanthone derivatives, 1,4,5,8-naphthalenebis-dicarboximide derivatives as described in U.S. Pat. Nos. 5,232,800,4,468,444, and 4,442,193 and phenylazoquinolide derivatives as describedin U.S. Pat. No. 6,472,514. In some embodiments of interest, theelectron transport compound comprises an(alkoxycarbonyl-9-fluorenylidene)malononitrile derivative, such as(4-n-butoxycarbonyl-9-fluorenylidene)malononitrile, and1,4,5,8-naphthalene bis-dicarboximide derivatives.

Although there are many charge transport materials available, there is aneed for other charge transport materials to meet the variousrequirements of particular electrophotography applications.

In electrophotography applications, a charge-generating compound withinan organophotoreceptor absorbs light to form electron-hole pairs. Theseelectrons and holes can be transported over an appropriate time frameunder a large electric field to discharge locally a surface charge thatis generating the field. The discharge of the field at a particularlocation results in a surface charge pattern that essentially matchesthe pattern drawn with the light. This charge pattern then can be usedto guide toner deposition. The charge transport materials describedherein are especially effective at transporting charge, and inparticular holes from the electron-hole pairs formed by the chargegenerating compound. In some embodiments, a specific electron transportcompound or charge transport compound can also be used along with thecharge transport material of this invention.

The layer or layers of materials containing the charge generatingcompound and the charge transport materials are within anorganophotoreceptor. To print a two dimensional image using theorganophotoreceptor, the organophotoreceptor has a two dimensionalsurface for forming at least a portion of the image. The imaging processthen continues by cycling the organophotoreceptor to complete theformation of the entire image and/or for the processing of subsequentimages.

The organophotoreceptor may be provided in the form of a plate, aflexible belt, a disk, a rigid drum, a sheet around a rigid or compliantdrum, or the like. The charge transport material can be in the samelayer as the charge generating compound and/or in a different layer fromthe charge generating compound. Additional layers can be used also, asdescribed further below.

In some embodiments, the organophotoreceptor material comprises, forexample: (a) a charge transport layer comprising the charge transportmaterial and a polymeric binder; (b) a charge generating layercomprising the charge generating compound and a polymeric binder; and(c) the electrically conductive substrate. The charge transport layermay be intermediate between the charge generating layer and theelectrically conductive substrate. Alternatively, the charge generatinglayer may be intermediate between the charge transport layer and theelectrically conductive substrate. In further embodiments, theorganophotoreceptor material has a single layer with both a chargetransport material and a charge generating compound within a polymericbinder.

The organophotoreceptors can be incorporated into an electrophotographicimaging apparatus, such as laser printers. In these devices, an image isformed from physical embodiments and converted to a light image that isscanned onto the organophotoreceptor to form a surface latent image. Thesurface latent image can be used to attract toner onto the surface ofthe organophotoreceptor, in which the toner image is the same or thenegative of the light image projected onto the organophotoreceptor. Thetoner can be a liquid toner or a dry toner. The toner is subsequentlytransferred, from the surface of the organophotoreceptor, to a receivingsurface, such as a sheet of paper. After the transfer of the toner, thesurface is discharged, and the material is ready to cycle again. Theimaging apparatus can further comprise, for example, a plurality ofsupport rollers for transporting a paper receiving medium and/or formovement of the photoreceptor, a light imaging component with suitableoptics to form the light image, a light source, such as a laser, a tonersource and delivery system and an appropriate control system.

An electrophotographic imaging process generally can comprise (a)applying an electrical charge to a surface of the above-describedorganophotoreceptor; (b) imagewise exposing the surface of theorganophotoreceptor to radiation to dissipate charge in selected areasand thereby form a pattern of charged and uncharged areas on thesurface; (c) exposing the surface with a toner, such as a liquid tonerthat includes a dispersion of colorant particles in an organic liquid tocreate a toner image, to attract toner to the charged or dischargedregions of the organophotoreceptor; and (d) transferring the toner imageto a substrate.

As described herein, an organophotoreceptor comprises a charge transportmaterial having the formula:

where R₁ and R₂ are, each independently, an alkyl group, an alkenylgroup, an alkynyl group, an aromatic group, or a heterocyclic group;

R₃ and R₄ are, each independently, H, an alkyl group, an alkenyl group,an alkynyl group, an aromatic group, or a heterocyclic group;

X₁ and X₂ are, each independently, a linking group, such as a—(CH₂)_(m)— group, where m is an integer between 1 and 20, inclusive,and one or more of the methylene groups is optionally replaced by O, S,N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, anNR_(a) group, a CR_(b) group, a CR_(c)R_(d) group, or a SiR_(e)R_(f)where R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) are, eachindependently, a bond, H, a hydroxyl group, a thiol group, a carboxylgroup, an amino group, an alkyl group, an alkoxy group, an alkenylgroup, an alkynyl group, a heterocyclic group, an aromatic group, or apart of a ring group, such as cycloalkyl groups, heterocyclic groups, ora benzo group;

Y₁ and Y₂, each independently, comprise an arylamine group, such as acarbazole group, a julolidine group, and an (N,N-disubstituted)arylaminegroup; and

Z is a bridging group having the formula -Q₁-X₃-Q₂- where Q₁ and Q₂comprise, each independently, O, S, or NR where R is H, an alkyl group,an alkenyl group, an alkynyl group, a heterocyclic group, or an aromaticgroup; and X₃ comprises a —(CH₂)_(p)— group where p is an integerbetween 1 and 20, inclusive, and at least one of the methylene groups isreplaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h)group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i),R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxylgroup, a thiol group, a carboxyl group, an amino group, an alkyl group,an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclicgroup, an aromatic group, or a part of a ring group, such as cycloalkylgroups, heterocyclic groups, or a benzo group.

A heterocyclic group includes any monocyclic or polycyclic (e.g.,bicyclic, tricyclic, etc.) ring compound having at least a heteroatom(e.g., O, S, N, P, B, Si, etc.) in the ring.

An aromatic group can be any conjugated ring system containing 4n+2pi-electrons. There are many criteria available for determiningaromaticity. A widely employed criterion for the quantitative assessmentof aromaticity is the resonance energy. Specifically, an aromatic grouphas a resonance energy. In some embodiments, the resonance energy of thearomatic group is at least 10 KJ/mol. In further embodiments, theresonance energy of the aromatic group is greater than 0.1 KJ/mol.Aromatic groups may be classified as an aromatic heterocyclic groupwhich contains at least a heteroatom in the 4n+2 pi-electron ring, or asan aryl group which does not contain a heteroatom in the 4n+2pi-electron ring. The aromatic group may comprise a combination ofaromatic heterocyclic group and aryl group. Nonetheless, either thearomatic heterocyclic or the aryl group may have at least one heteroatomin a substituent attached to the 4n+2 pi-electron ring. Furthermore,either the aromatic heterocyclic or the aryl group may comprise amonocyclic or polycyclic (such as bicyclic, tricyclic, etc.) ring.

Non-limiting examples of the aromatic heterocyclic group are furanyl,thiophenyl, pyrrolyl, indolyl, carbazolyl, benzofuranyl,benzothiophenyl, dibenzofuranyl, dibenzothiophenyl, pyridinyl,pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, tetrazinyl, petazinyl,quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl, quinazolinyl,quinoxalinyl, naphthyridinyl, acridinyl, phenanthridinyl,phenanthrolinyl, anthyridinyl, purinyl, pteridinyl, alloxazinyl,phenazinyl, phenothiazinyl, phenoxazinyl, phenoxathiinyl,dibenzo(1,4)dioxinyl, thianthrenyl, and a combination thereof. Thearomatic heterocyclic group may also include any combination of theabove aromatic heterocyclic groups bonded together either by a bond (asin bicarbazolyl) or by a linking group (as in 1,6di(10H-10-phenothiazinyl)hexane). The linking group may include analiphatic group, an aromatic group, a heterocyclic group, or acombination thereof. Furthermore, the linking group may comprise atleast one heteroatom such as O, S, Si, and N.

Non-limiting examples of the aryl group are phenyl, naphthyl, benzyl, ortolanyl group, sexiphenylene, phenanthrenyl, anthracenyl, coronenyl, andtolanylphenyl. The aryl group may also include any combination of theabove aryl groups bonded together either by a bond (as in biphenylgroup) or a linking group (as in stilbenyl, diphenyl sulfone, anarylamine group). The linking group may include an aliphatic group, anaromatic group, a heterocyclic group, or a combination thereof.Furthermore, the linking group may comprise at least one heteroatom suchas O, S, Si, and N.

Substitution is liberally allowed on the chemical groups to affectvarious physical effects on the properties of the compounds, such asmobility, sensitivity, solubility, stability, and the like, as is knowngenerally in the art. In the description of chemical substituents, thereare certain practices common to the art that are reflected in the use oflanguage. The term group indicates that the generically recited chemicalentity (e.g., alkyl group, phenyl group, aromatic group, arylaminegroup, julolidine group, carbazole group, (N,N-disubstituted)arylaminegroup, etc.) may have any substituent thereon which is consistent withthe bond structure of that group. For example, where the term ‘alkylgroup’ is used, that term would not only include unsubstituted linear,branched and cyclic alkyls, such as methyl, ethyl, isopropyl,tert-butyl, cyclohexyl, dodecyl and the like, but also substituentshaving heteroatom, such as 3-ethoxy]propyl, 4-(N,N-diethylamino)butyl,3-hydroxypentyl, 2-thiolhexyl, 1,2,3-tribromoopropyl, and the like, andaromatic group, such as phenyl, naphthyl, carbazolyl, pyrrole, and thelike. However, as is consistent with such nomenclature, no substitutionwould be included within the term that would alter the fundamental bondstructure of the underlying group. For example, where a phenyl group isrecited, substitution such as 2- or 4-aminophenyl, 2- or4-(N,N-disubstituted)aminophenyl, 2,4-dihydroxyphenyl,2,4,6-trithiophenyl, 2,4,6-trimethoxyphenyl and the like would beacceptable within the terminology, while substitution of1,1,2,2,3,3-hexamethylphenyl would not be acceptable as thatsubstitution would require the ring bond structure of the phenyl groupto be altered to a non-aromatic form. Where the term moiety is used,such as alkyl moiety or phenyl moiety, that terminology indicates thatthe chemical material is not substituted. Where the term alkyl moiety isused, that term represents only an unsubstituted alkyl hydrocarbongroup, whether branched, straight chain, or cyclic.

Organophotoreceptors

The organophotoreceptor may be, for example, in the form of a plate, asheet, a flexible belt, a disk, a rigid drum, or a sheet around a rigidor compliant drum, with flexible belts and rigid drums generally beingused in commercial embodiments. The organophotoreceptor may comprise,for example, an electrically conductive substrate and on theelectrically conductive substrate a photoconductive element in the formof one or more layers. The photoconductive element can comprise both acharge transport material and a charge generating compound in apolymeric binder, which may or may not be in the same layer, as well asa second charge transport material such as a charge transport compoundor an electron transport compound in some embodiments. For example, thecharge transport material and the charge generating compound can be in asingle layer. In other embodiments, however, the photoconductive elementcomprises a bilayer construction featuring a charge generating layer anda separate charge transport layer. The charge generating layer may belocated intermediate between the electrically conductive substrate andthe charge transport layer. Alternatively, the photoconductive elementmay have a structure in which the charge transport layer is intermediatebetween the electrically conductive substrate and the charge generatinglayer.

The electrically conductive substrate may be flexible, for example inthe form of a flexible web or a belt, or inflexible, for example in theform of a drum. A drum can have a hollow cylindrical structure thatprovides for attachment of the drum to a drive that rotates the drumduring the imaging process. Typically, a flexible electricallyconductive substrate comprises an electrically insulating substrate anda thin layer of electrically conductive material onto which thephotoconductive material is applied.

The electrically insulating substrate may be paper or a film formingpolymer such as polyester (e.g., polyethylene terephthalate orpolyethylene naphthalate), polyimide, polysulfone, polypropylene, nylon,polyester, polycarbonate, polyvinyl resin, polyvinyl fluoride,polystyrene and the like. Specific examples of polymers for supportingsubstrates included, for example, polyethersulfone (STABAR™ S-100,available from ICI), polyvinyl fluoride (Tedlar®, available from E.I.DuPont de Nemours & Company), polybisphenol-A polycarbonate (MAKROFOL™,available from Mobay Chemical Company) and amorphous polyethyleneterephthalate (MELINAR™, available from ICI Americas, Inc.). Theelectrically conductive materials may be graphite, dispersed carbonblack, iodine, conductive polymers such as polypyrroles and Calgon®conductive polymer 261 (commercially available from Calgon Corporation,Inc., Pittsburgh, Pa.), metals such as aluminum, titanium, chromium,brass, gold, copper, palladium, nickel, or stainless steel, or metaloxide such as tin oxide or indium oxide. In embodiments of particularinterest, the electrically conductive material is aluminum. Generally,the photoconductor substrate has a thickness adequate to provide therequired mechanical stability. For example, flexible web substratesgenerally have a thickness from about 0.01 to about 1 mm, while drumsubstrates generally have a thickness from about 0.5 mm to about 2 mm.

The charge generating compound is a material that is capable ofabsorbing light to generate charge carriers (such as a dye or pigment).Non-limiting examples of suitable charge generating compounds include,for example, metal-free phthalocyanines (e.g., ELA 8034 metal-freephthalocyanine available from H.W. Sands, Inc. or Sanyo Color Works,Ltd., CGM-X01), metal phthalocyanines such as titanium phthalocyanine,copper phthalocyanine, oxytitanium phthalocyanine (also referred to astitanyl oxyphthalocyanine, and including any crystalline phase ormixtures of crystalline phases that can act as a charge generatingcompound), hydroxygallium phthalocyanine, squarylium dyes and pigments,hydroxy-substituted squarylium pigments, perylimides, polynuclearquinones available from Allied Chemical Corporation under the trade nameINDOFAST™ Double Scarlet, INDOFAST™ Violet Lake B, INDOFAST™ BrilliantScarlet and INDOFAST™ Orange, quinacridones available from DuPont underthe trade name MONASTRAL™ Red, MONASTRAL™ Violet and MONASTRAL™ Red Y,naphthalene 1,4,5,8-tetracarboxylic acid derived pigments including theperinones, tetrabenzoporphyrins and tetranaphthaloporphyrins, indigo-and thioindigo dyes, benzothioxanthene-derivatives, perylene3,4,9,10-tetracarboxylic acid derived pigments, polyazo-pigmentsincluding bisazo-, trisazo- and tetrakisazo-pigments, polymethine dyes,dyes containing quinazoline groups, tertiary amines, amorphous selenium,selenium alloys such as selenium-tellurium, selenium-tellurium-arsenicand selenium-arsenic, cadmium sulphoselenide, cadmium selenide, cadmiumsulphide, and mixtures thereof. For some embodiments, the chargegenerating compound comprises oxytitanium phthalocyanine (e.g., anyphase thereof), hydroxygallium phthalocyanine or a combination thereof.

The photoconductive layer of this invention may optionally contain asecond charge transport material which may be a charge transportcompound, an electron transport compound, or a combination of both.Generally, any charge transport compound or electron transport compoundknown in the art can be used as the second charge transport material.

An electron transport compound and a UV light stabilizer can have asynergistic relationship for providing desired electron flow within thephotoconductor. The presence of the UV light stabilizers alters theelectron transport properties of the electron transport compounds toimprove the electron transporting properties of the composite. UV lightstabilizers can be ultraviolet light absorbers or ultraviolet lightinhibitors that trap free radicals.

UV light absorbers can absorb ultraviolet radiation and dissipate it asheat. UV light inhibitors are thought to trap free radicals generated bythe ultraviolet light and after trapping of the free radicals,subsequently to regenerate active stabilizer moieties with energydissipation. In view of the synergistic relationship of the UVstabilizers with electron transport compounds, the particular advantagesof the UV stabilizers may not be their UV stabilizing abilities,although the UV stabilizing ability may be further advantageous inreducing degradation of the organophotoreceptor over time. The improvedsynergistic performance of organophotoreceptors with layers comprisingboth an electron transport compound and a UV stabilizer are describedfurther in copending U.S. patent application Ser. No. 10/425,333 filedon Apr. 28, 2003 to Zhu, entitled “Organophotoreceptor With A LightStabilizer,” incorporated herein by reference.

Non-limiting examples of suitable light stabilizer include, for example,hindered trialkylamines such as Tinuvin 144 and Tinuvin 292 (from CibaSpecialty Chemicals, Terrytown, N.Y.), hindered alkoxydialkylamines suchas Tinuvin 123 (from Ciba Specialty Chemicals), benzotriazoles such asTinuvan 328, Tinuvin 900 and Tinuvin 928 (from Ciba SpecialtyChemicals), benzophenones such as Sanduvor 3041 (from Clariant Corp.,Charlotte, N.C.), nickel compounds such as Arbestab (from RobinsonBrothers Ltd, West Midlands, Great Britain), salicylates,cyanocinnamates, benzylidene malonates, benzoates, oxanilides such asSanduvor VSU (from Clariant Corp., Charlotte, N.C.), triazines such asCyagard UV-1164 (from Cytec Industries Inc., N.J.), polymeric stericallyhindered amines such as Luchem (from Atochem North America, Buffalo,N.Y.). In some embodiments, the light stabilizer is selected from thegroup consisting of hindered trialkylamines having the followingformula:

where R₁, R₂, R₃, R₄, R₆, R₇, R₈, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅ are, eachindependently, hydrogen, alkyl group, or ester, or ether group; and R₅,R₉, and R₁₄ are, each independently, alkyl group; and X is a linkinggroup selected from the group consisting of —O—CO—(CH₂)_(m)—CO—O— wherem is between 2 to 20.

The binder generally is capable of dispersing or dissolving the chargetransport material (in the case of the charge transport layer or asingle layer construction), the charge generating compound (in the caseof the charge generating layer or a single layer construction) and/or anelectron transport compound for appropriate embodiments. Examples ofsuitable binders for both the charge generating layer and chargetransport layer generally include, for example,polystyrene-co-butadiene, polystyrene-co-acrylonitrile, modified acrylicpolymers, polyvinyl acetate, styrene-alkyd resins, soya-alkyl resins,polyvinylchloride, polyvinylidene chloride, polyacrylonitrile,polycarbonates, polyacrylic acid, polyacrylates, polymethacrylates,styrene polymers, polyvinyl butyral, alkyd resins, polyamides,polyurethanes, polyesters, polysulfones, polyethers, polyketones,phenoxy resins, epoxy resins, silicone resins, polysiloxanes,poly(hydroxyether) resins, polyhydroxystyrene resins, novolak,poly(phenylglycidyl ether)-co-dicyclopentadiene, copolymers of monomersused in the above-mentioned polymers, and combinations thereof. Specificsuitable binders include, for example, polyvinyl butyral, polycarbonate,and polyester. Non-limiting examples of polyvinyl butyral include BX-1and BX-5 from Sekisui Chemical Co. Ltd., Japan. Non-limiting examples ofsuitable polycarbonate include polycarbonate A which is derived frombisphenol-A (e.g. Iupilon-A from Mitsubishi Engineering Plastics, orLexan 145 from General Electric); polycarbonate Z which is derived fromcyclohexylidene bisphenol (e.g. Iupilon-Z from Mitsubishi EngineeringPlastics Corp, White Plain, N.Y.); and polycarbonate C which is derivedfrom methylbisphenol A (from Mitsubishi Chemical Corporation).Non-limiting examples of suitable polyester binders includeortho-polyethylene terephthalate (e.g. OPET TR-4 from Kanebo Ltd.,Yamaguchi, Japan).

Suitable optional additives for any one or more of the layers include,for example, antioxidants, coupling agents, dispersing agents, curingagents, surfactants, and combinations thereof.

The photoconductive element overall typically has a thickness from about10 microns to about 45 microns. In the dual layer embodiments having aseparate charge generating layer and a separate charge transport layer,charge generation layer generally has a thickness form about 0.5 micronsto about 2 microns, and the charge transport layer has a thickness fromabout 5 microns to about 35 microns. In embodiments in which the chargetransport material and the charge generating compound are in the samelayer, the layer with the charge generating compound and the chargetransport composition generally has a thickness from about 7 microns toabout 30 microns. In embodiments with a distinct electron transportlayer, the electron transport layer has an average thickness from about0.5 microns to about 10 microns and in further embodiments from about 1micron to about 3 microns. In general, an electron transport overcoatlayer can increase mechanical abrasion resistance, increases resistanceto carrier liquid and atmospheric moisture, and decreases degradation ofthe photoreceptor by corona gases. A person of ordinary skill in the artwill recognize that additional ranges of thickness within the explicitranges above are contemplated and are within the present disclosure.

Generally, for the organophotoreceptors described herein, the chargegeneration compound is in an amount from about 0.5 to about 25 weightpercent, in further embodiments in an amount from about 1 to about 15weight percent, and in other embodiments in an amount from about 2 toabout 10 weight percent, based on the weight of the photoconductivelayer. The charge transport material is in an amount from about 10 toabout 80 weight percent, based on the weight of the photoconductivelayer, in further embodiments in an amount from about 35 to about 60weight percent, and in other embodiments from about 45 to about 55weight percent, based on the weight of the photoconductive layer. Theoptional second charge transport material, when present, can be in anamount of at least about 2 weight percent, in other embodiments fromabout 2.5 to about 25 weight percent, based on the weight of thephotoconductive layer, and in further embodiments in an amount fromabout 4 to about 20 weight percent, based on the weight of thephotoconductive layer. The binder is in an amount from about 15 to about80 weight percent, based on the weight of the photoconductive layer, andin further embodiments in an amount from about 20 to about 75 weightpercent, based on the weight of the photoconductive layer. A person ofordinary skill in the art will recognize that additional ranges withinthe explicit ranges of compositions are contemplated and are within thepresent disclosure.

For the dual layer embodiments with a separate charge generating layerand a charge transport layer, the charge generation layer generallycomprises a binder in an amount from about 10 to about 90 weightpercent, in further embodiments from about 15 to about 80 weight percentand in some embodiments in an amount from about 20 to about 75 weightpercent, based on the weight of the charge generation layer. Theoptional charge transport material in the charge generating layer, ifpresent, generally can be in an amount of at least about 2.5 weightpercent, in further embodiments from about 4 to about 30 weight percentand in other embodiments in an amount from about 10 to about 25 weightpercent, based on the weight of the charge generating layer. The chargetransport layer generally comprises a binder in an amount from about 20weight percent to about 70 weight percent and in further embodiments inan amount from about 30 weight percent to about 50 weight percent. Aperson of ordinary skill in the art will recognize that additionalranges of binder concentrations for the dual layer embodiments withinthe explicit ranges above are contemplated and are within the presentdisclosure.

For the embodiments with a single layer having a charge generatingcompound and a charge transport material, the photoconductive layergenerally comprises a binder, a charge transport material, and a chargegeneration compound. The charge generation compound can be in an amountfrom about 0.05 to about 25 weight percent and in further embodiment inan amount from about 2 to about 15 weight percent, based on the weightof the photoconductive layer. The charge transport material can be in anamount from about 10 to about 80 weight percent, in other embodimentsfrom about 25 to about 65 weight percent, in additional embodiments fromabout 30 to about 60 weight percent and in further embodiments in anamount from about 35 to about 55 weight percent, based on the weight ofthe photoconductive layer, with the remainder of the photoconductivelayer comprising the binder, and optionally additives, such as anyconventional additives. A single layer with a charge transportcomposition and a charge generating compound generally comprises abinder in an amount from about 10 weight percent to about 75 weightpercent, in other embodiments from about 20 weight percent to about 60weight percent, and in further embodiments from about 25 weight percentto about 50 weight percent. Optionally, the layer with the chargegenerating compound and the charge transport material may comprise asecond charge transport material. The optional second charge transportmaterial, if present, generally can be in an amount of at least about2.5 weight percent, in further embodiments from about 4 to about 30weight percent and in other embodiments in an amount from about 10 toabout 25 weight percent, based on the weight of the photoconductivelayer. A person of ordinary skill in the art will recognize thatadditional composition ranges within the explicit compositions rangesfor the layers above are contemplated and are within the presentdisclosure.

In general, any layer with an electron transport layer canadvantageously further include a UV light stabilizer. In particular, theelectron transport layer generally can comprise an electron transportcompound, a binder, and an optional UV light stabilizer. An overcoatlayer comprising an electron transport compound is described further incopending U.S. patent application Ser. No. 10/396,536 to Zhu et al.entitled, “Organophotoreceptor With An Electron Transport Layer,”incorporated herein by reference. For example, an electron transportcompound as described above may be used in the release layer of thephotoconductors described herein. The electron transport compound in anelectron transport layer can be in an amount from about 10 to about 50weight percent, and in other embodiments in an amount from about 20 toabout 40 weight percent, based on the weight of the electron transportlayer. A person of ordinary skill in the art will recognize thatadditional ranges of compositions within the explicit ranges arecontemplated and are within the present disclosure.

The UV light stabilizer, if present, in any one or more appropriatelayers of the photoconductor generally is in an amount from about 0.5 toabout 25 weight percent and in some embodiments in an amount from about1 to about 10 weight percent, based on the weight of the particularlayer. A person of ordinary skill in the art will recognize thatadditional ranges of compositions within the explicit ranges arecontemplated and are within the present disclosure.

For example, the photoconductive layer may be formed by dispersing ordissolving the components, such as one or more of a charge generatingcompound, the charge transport material of this invention, a secondcharge transport material such as a charge transport compound or anelectron transport compound, a UV light stabilizer, and a polymericbinder in organic solvent, coating the dispersion and/or solution on therespective underlying layer and drying the coating. In particular, thecomponents can be dispersed by high shear homogenization, ball-milling,attritor milling, high energy bead (sand) milling or other sizereduction processes or mixing means known in the art for effectingparticle size reduction in forming a dispersion.

The photoreceptor may optionally have one or more additional layers aswell. An additional layer can be, for example, a sub-layer or anovercoat layer, such as a barrier layer, a release layer, a protectivelayer, or an adhesive layer. A release layer or a protective layer mayform the uppermost layer of the photoconductor element. A barrier layermay be sandwiched between the release layer and the photoconductiveelement or used to overcoat the photoconductive element. The barrierlayer provides protection from abrasion to the underlayers. An adhesivelayer locates and improves the adhesion between a photoconductiveelement, a barrier layer and a release layer, or any combinationthereof. A sub-layer is a charge blocking layer and locates between theelectrically conductive substrate and the photoconductive element. Thesub-layer may also improve the adhesion between the electricallyconductive substrate and the photoconductive element.

Suitable barrier layers include, for example, coatings such ascrosslinkable siloxanol-colloidal silica coating and hydroxylatedsilsesquioxane-colloidal silica coating, and organic binders such aspolyvinyl alcohol, methyl vinyl ether/maleic anhydride copolymer,casein, polyvinyl pyrrolidone, polyacrylic acid, gelatin, starch,polyurethanes, polyimides, polyesters, polyamides, polyvinyl acetate,polyvinyl chloride, polyvinylidene chloride, polycarbonates, polyvinylbutyral, polyvinyl acetoacetal, polyvinyl formal, polyacrylonitrile,polymethyl methacrylate, polyacrylates, polyvinyl carbazoles, copolymersof monomers used in the above-mentioned polymers, vinyl chloride/vinylacetate/vinyl alcohol terpolymers, vinyl chloride/vinyl acetate/maleicacid terpolymers, ethylene/vinyl acetate copolymers, vinylchloride/vinylidene chloride copolymers, cellulose polymers, andmixtures thereof. The above barrier layer polymers optionally maycontain small inorganic particles such as fumed silica, silica, titania,alumina, zirconia, or a combination thereof. Barrier layers aredescribed further in U.S. Pat. No. 6,001,522 to Woo et al., entitled“Barrier Layer For Photoconductor Elements Comprising An Organic PolymerAnd Silica,” incorporated herein by reference. The release layer topcoatmay comprise any release layer composition known in the art. In someembodiments, the release layer is a fluorinated polymer, siloxanepolymer, fluorosilicone polymer, silane, polyethylene, polypropylene,polyacrylate, or a combination thereof. The release layers can comprisecrosslinked polymers.

The release layer may comprise, for example, any release layercomposition known in the art. In some embodiments, the release layercomprises a fluorinated polymer, siloxane polymer, fluorosiliconepolymer, polysilane, polyethylene, polypropylene, polyacrylate,poly(methyl methacrylate-co-methacrylic acid), urethane resins,urethane-epoxy resins, acrylated-urethane resins, urethane-acrylicresins, or a combination thereof. In further embodiments, the releaselayers comprise crosslinked polymers.

The protective layer can protect the organophotoreceptor from chemicaland mechanical degradation. The protective layer may comprise anyprotective layer composition known in the art. In some embodiments, theprotective layer is a fluorinated polymer, siloxane polymer,fluorosilicone polymer, polysilane, polyethylene, polypropylene,polyacrylate, poly(methyl methacrylate-co-methacrylic acid), urethaneresins, urethane-epoxy resins, acrylated-urethane resins,urethane-acrylic resins, or a combination thereof. In some embodimentsof particular interest, the release layers are crosslinked polymers.

An overcoat layer may comprise an electron transport compound asdescribed further in copending U.S. patent application Ser. No.10/396,536, filed on Mar. 25, 2003 to Zhu et al. entitled,“Organoreceptor With An Electron Transport Layer,” incorporated hereinby reference. For example, an electron transport compound, as describedabove, may be used in the release layer of this invention. The electrontransport compound in the overcoat layer can be in an amount from about2 to about 50 weight percent, and in other embodiments in an amount fromabout 10 to about 40 weight percent, based on the weight of the releaselayer. A person of ordinary skill in the art will recognize thatadditional ranges of composition within the explicit ranges arecontemplated and are within the present disclosure.

Generally, adhesive layers comprise a film forming polymer, such aspolyester, polyvinylbutyral, polyvinylpyrrolidone, polyurethane,polymethyl methacrylate, poly(hydroxy amino ether) and the like. Barrierand adhesive layers are described further in U.S. Pat. No. 6,180,305 toAckley et al., entitled “Organic Photoreceptors for LiquidElectrophotography,” incorporated herein by reference.

Sub-layers can comprise, for example, polyvinylbutyral, organosilanes,hydrolyzable silanes, epoxy resins, polyesters, polyamides,polyurethanes, cellulosics and the like. In some embodiments, thesub-layer has a dry thickness between about 20 Angstroms and about20,000 Angstroms. Sublayers containing metal oxide conductive particlescan be between about 1 and about 25 microns thick. A person of ordinaryskill in the art will recognize that additional ranges of compositionsand thickness within the explicit ranges are contemplated and are withinthe present disclosure.

The charge transport materials as described herein, and photoreceptorsincluding these compounds, are suitable for use in an imaging processwith either dry or liquid toner development. For example, any dry tonersand liquid toners known in the art may be used in the process and theapparatus of this invention. Liquid toner development can be desirablebecause it offers the advantages of providing higher resolution imagesand requiring lower energy for image fixing compared to dry toners.Examples of suitable liquid toners are known in the art. Liquid tonersgenerally comprise toner particles dispersed in a carrier liquid. Thetoner particles can comprise a colorant/pigment, a resin binder, and/ora charge director. In some embodiments of liquid toner, a resin topigment ratio can be from 1:1 to 10:1, and in other embodiments, from4:1 to 8:1. Liquid toners are described further in Published U.S. PatentApplications 2002/0128349, entitled “Liquid Inks Comprising A StableOrganosol,” and 2002/0086916, entitled “Liquid Inks Comprising TreatedColorant Particles,” and U.S. Pat. No. 6,649,316, entitled “Phase ChangeDeveloper For Liquid Electrophotography,” all three of which areincorporated herein by reference.

Charge Transport Material

As described herein, an organophotoreceptor comprises a charge transportmaterial having the formula

where R₁ and R₂ are, each independently, an alkyl group, an alkenylgroup, an alkynyl group, an aromatic group, or a heterocyclic group;

R₃ and R₄ are, each independently, H, an alkyl group, an alkenyl group,an alkynyl group, an aromatic group, or a heterocyclic group;

X₁ and X₂ are, each independently, a linking group, such as a—(CH₂)_(m)— group, where m is an integer between 1 and 20, inclusive,and one or more of the methylene groups is optionally replaced by O, S,N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, anNR_(a) group, a CR_(b) group, a CR_(c)R_(d) group, or a SiR_(e)R_(f)where R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) are, eachindependently, a bond, H, a hydroxyl group, a thiol group, a carboxylgroup, an amino group, an alkyl group, an alkoxy group, an alkenylgroup, an alkynyl group, a heterocyclic group, an aromatic group, or apart of a ring group, such as cycloalkyl groups, heterocyclic groups, ora benzo group;

Y₁ and Y₂, each independently, comprise an arylamine group, such as acarbazole group, a julolidine group, and an (N,N-disubstituted)arylaminegroup; and

Z is a bridging group having the formula -Q₁-X₃-Q₂- where Q₁ and Q₂comprise, each independently, O, S, or NR where R is H, an alkyl group,an alkenyl group, an alkynyl group, a heterocyclic group, or an aromaticgroup; and X₃ comprises a —(CH₂)_(p)— group where p is an integerbetween 1 and 20, inclusive, and at least one of the methylene groups isreplaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h)group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i),R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxylgroup, a thiol group, a carboxyl group, an amino group, an alkyl group,an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclicgroup, an aromatic group, or a part of a ring group, such as cycloalkylgroups, heterocyclic groups, or a benzo group.

With respect to Formula (I), substitution is liberally allowed,especially on Z, X₁, X₂, Y₁, and Y₂. Variation of the substituents, suchas an aromatic group, an alkyl group, a heterocyclic group, and a ringgroup such as a benzo group, on Z, X₁, X₂, Y₁, and Y₂ can result invarious physical effects on the properties of the compounds, such asmobility, solubility, compatibility, stability, spectral absorbance,dispersibility, and the like, including, for example, substitutionsknown in the art to effect particular modifications.

The charge transport material of Formula (I) may be symmetrical orunsymmetrical. Thus, for example, X₁ and X₂ may be the same ordifferent. Similarly, Y₁ and Y₂ may be the same or different; R₁ and R₂may be the same or different; R₃ and R₄ may be the same or different; orZ may be symmetrical or unsymmetrical. In addition, Formula (I) for thecharge transport material is intended to cover isomers.

In some embodiments, the organophotoreceptors as described herein cancomprise an improved charge transport material of Formula (I) where X₁and X₂ are, each independently, a —CH₂—CH(Q₃H)—CH₂— group where Q₃comprises O, S or NR′, where R′ is hydrogen, an alkyl group, an alkenylgroup, an alkynyl group, or an aromatic group; and Y₁ and Y₂ are, eachindependently, an (N,N-disubstituted)arylamine group. In some furtherembodiments, Q₁ and Q₂ are, each independently, S; and X₃ is a—CH₂—CH(Q₄H)—CH(Q₅H)—CH₂— group, a —CH(R₅)—CH(R₆)— group, or a—CH₂—CH₂-Q₆-CH₂—CH₂-Q₇-CH₂—CH₂— group where R₅ and R₆ are, eachindependently, an alkyl group, an alkenyl group, an alkynyl group, aheterocyclic group, an aromatic group, or a part of a ring group; andQ₄, Q₅, Q₆, and Q₇, are, each independently, O, S, or NR″ where R″ is H,an alkyl group, an alkenyl group, an alkynyl group, a heterocyclicgroup, or an aromatic group. Specific, non-limiting examples of suitablecharge transport materials within Formula (I) of the present inventionhave the following structures:

Synthesis Of Charge Transport Materials

The synthesis of the charge transport materials of this invention can beprepared by the following multi-step synthetic procedures, althoughother suitable procedures can be used by a person of ordinary skill inthe art based on the disclosure herein.

General Synthetic Procedure for Charge Transport Materials of Formula(I)

The charge transport materials of Formula (I) may be prepared by thering-opening reaction of at least an arylamine hydrazone compound havinga reactive ring group (E₁ or E₂) with a bridging compound, H-Q₁-X₃-Q₂-H,having at least two functional groups (Q₁H and Q₂H) that are reactivetoward the reactive ring group. The functional groups may be selectedfrom the group consisting of a hydroxyl group, a thiol group, aminogroups, and a carboxyl group. The preparations of the arylaminehydrazone compound having a reactive ring group have been disclosed inU.S. patent application Ser. Nos. 0/634,164 and 10/749,178, which areincorporated herein by reference.

The reactive ring group may be selected from the group consisting ofheterocyclic ring groups which have a higher strain energy than itscorresponding open-ring structure. The conventional definition of strainenergy is that it represents the difference in energy between the actualmolecule and a completely strain-free molecule of the same constitution.More information about the origin of strain energy can be found in thearticle by Wiberg et al., “A Theoretical Analysis of HydrocarbonProperties: II Additivity of Group Properties and the Origin of StrainEnergy,” J. Am. Chem. Soc. 109, 985 (1987). The above article isincorporated herein by reference. The heterocyclic ring group may have3, 4, 5, 7, 8, 9, 10, 11, or 12 members, in further embodiments 3, 4, 5,7, or 8 members, in some embodiment 3, 4, or 8 members, and inadditional embodiments 3 or 4 members. Non-limiting examples of suchheterocyclic ring are cyclic ethers (e.g., epoxides and oxetane), cyclicamines (e.g., aziridine), cyclic sulfides (e.g., thiirane), cyclicamides (e.g., 2-azetidinone, 2-pyrrolidone, 2-piperidone, caprolactam,enantholactam, and capryllactam), N-carboxy-α-amino acid anhydrides,lactones, and cyclosiloxanes. The chemistry of the above heterocyclicrings is described in George Odian, “Principle of Polymerization,”second edition, Chapter 7, p. 508–552 (1981), incorporated herein byreference.

In some embodiments of interest, the reactive ring group is selectedfrom the group consisting of an epoxy group, a thiiranyl group, anaziridino group, and an oxetanyl group.

In further embodiments, the reactive ring group is an epoxy group. Theepoxy group may be introduced by reacting an arylamine hydrazonecompound with an organic halide comprising an epoxy group to form thecorresponding arylamine hydrazone compound having an epoxy group.Non-limiting examples of suitable organic halide comprising an epoxygroup as the reactive ring group are epihalohydrins, such asepichlorohydrin. The organic halide comprising an epoxy group can alsobe prepared by the epoxidation reaction of the corresponding alkenehaving a halide group. Such epoxidation reaction is described in Careyet al., “Advanced Organic Chemistry, Part B: Reactions and Synthesis,”New York, 1983, pp. 494–498, incorporated herein by reference. Thealkene having a halide group can be prepared by the Wittig reactionbetween a suitable aldehyde or keto compound and a suitable Wittigreagent. The Wittig and related reactions are described in Carey et al.,“Advanced Organic Chemistry, Part B: Reactions and Synthesis,” New York,1983, pp. 69–77, which is incorporated herein by reference.

In other embodiments, the reactive ring group is a thiiranyl group. Thearylamine hydrazone compounds having an epoxy group, such as thosedescribed above, can be converted into the corresponding thiiranylcompound by refluxing the epoxy compound and ammonium thiocyanate intetrahydrofuran. Alternatively, the corresponding thiiranyl compound maybe obtained by passing a solution of the above-described epoxy compoundthrough 3-(thiocyano)propyl-functionalized silica gel (commerciallyavailable form Aldrich, Milwaukee, Wis.). Alternatively, a thiiranylcompound may be obtained by the thia-Payne rearrangement of acorresponding epoxy compound. The thia-Payne rearrangement is describedin Rayner, C. M. Synlett 1997, 11; Liu, Q. Y.; Marchington, A. P.;Rayner, C. M. Tetrahedron 1997, 53, 15729; Ibuka, T. Chem. Soc. Rev.1998, 27, 145; and Rayner, C. M. Contemporary Organic Synthesis 1996, 3,499. All the above four articles are incorporated herein by reference.

In other embodiments, the reactive ring group is an aziridinyl group. Anaziridine compound may be obtained by the aza-Payne rearrangement of acorresponding arylamine hydrazone compounds having an epoxy group, suchas one of those epoxy compounds described above. The thia-Paynerearrangement is described in Rayner, C. M. Synlett 1997, 11; Liu, Q.Y.; Marchington, A. P.; Rayner, C. M. Tetrahedron 1997, 53, 15729; andIbuka, T. Chem. Soc. Rev. 1998, 27, 145. All the above three articlesare incorporated herein by reference. Alternatively, an aziridinecompound may be prepared by the addition reaction between a suitablenitrene compound and a suitable alkene. Such addition reaction isdescribed in Carey et al., “Advanced Organic Chemistry, Part B:Reactions and Synthesis,” New York, 1983, pp. 446–448, incorporatedherein by reference.

In other embodiments, the reactive ring group is an oxetanyl group. Anoxetane compound may be prepared by the Paterno-Buchi reaction between asuitable carbonyl compound and a suitable alkene. The Paterno-Buchireaction is described in Carey et al., “Advanced Organic Chemistry, PartB: Reactions and Synthesis,” New York, 1983, pp. 335–336, incorporatedherein by reference.

The bridging compound may have the formula HQ₁-X₃-Q₂H where Q₁ and Q₂comprise, each independently, O, S, or NR where R is H, an alkyl group,an alkenyl group, an alkynyl group, a heterocyclic group, or an aromaticgroup; and X₃ comprises a —(CH₂)_(p)— group where p is an integerbetween 1 and 20, inclusive, and at least one of the methylene groups isreplaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h)group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i),R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxylgroup, a thiol group, a carboxyl group, an amino group, an alkyl group,an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclicgroup, an aromatic group, or a part of a ring group, such as cycloalkylgroups, heterocyclic groups, or a benzo group. In further embodiments,X₃ is a —CH₂—CH(Q₄H)—CH(Q₅H)—CH₂— group, a —CH(R₅)—CH(R₆)— group, or a—CH₂—CH₂-Q₆-CH₂—CH₂-Q₇-CH₂—CH₂— group where R₅ and R₆ are, eachindependently, an alkyl group, an alkenyl group, an alkynyl group, aheterocyclic group, an aromatic group, or a part of a ring group; andQ₄, Q₅, Q₆, and Q₇, are, each independently, O, S, or NR″ where R″ is H,an alkyl group, an alkenyl group, an alkynyl group, a heterocyclicgroup, or an aromatic group.

In some embodiments, the bridging compound may be a diol, a dithiol, adiamine, a dicarboxylic acid, a hydroxylamine, an amino acid, a hydroxylacid, a thiol acid, a hydroxythiol, or a thioamine. Non-limitingexamples of suitable dithiol are 3,6-dioxa-1,8-octanedithiol,erythro-1,4-dimercapto-2,3-butanediol,(±)-threo-1,4-dimercapto-2,3-butanediol, 4,4′-thiobisbenzenethiol,1,4-benzenedithiol, 1,3-benzenedithiol, sulfonyl-bis(benzenethiol),2,5-dimecapto-1,3,4-thiadiazole, 1,2-ethanedithiol, 1,3-propanedithiol,1,4-butanedithiol, 2,3-butanedithiol, 1,5-pentanedithiol, and1,6-hexanedithiol. Non-limiting examples of suitable diols are2,2′-bi-7-naphtol, 1,4-dihydroxybenzene, 1,3-dihydroxybenzene,10,10-bis(4-hydroxyphenyl)anthrone, 4,4′-sulfonyldiphenol, bisphenol,4,4′-(9-fluorenylidene)diphenol, 1,10-decanediol, 1,5-pentanediol,diethylene glycol, 4,4′-(9-fluorenylidene)-bis(2-phenoxyethanol),bis(2-hydroxyethyl)terephthalate, bis[4-(2-hydroxyethoxy)phenyl]sulfone,hydroquinone-bis(2-hydroxyethyl)ether, andbis(2-hydroxyethyl)piperazine. Non-limiting examples of suitable diamineare diaminoarenes, and diaminoalkanes. Non-limiting examples of suitabledicarboxylic acid are phthalic acid, terephthalic acid, adipic acid, and4,4′-biphenyldicarboxylic acid. Non-limiting examples of suitablehydroxylamine are p-aminophenol and fluoresceinamine. Non-limitingexamples of suitable amino acid are 4-aminobutyric acid, phenylalanine,and 4-aminobenzoic acid. Non-limiting examples of suitable hydroxyl acidare salicylic acid, 4-hydroxybutyric acid, and 4-hydroxybenzoic acid.Non-limiting examples of suitable hydroxythiol are monothiohydroquinoneand 4-mercapto-1-butanol. Non-limiting example of suitable thioamine isp-aminobenzenethiol. Non-limiting example of suitable thiol acid are4-mercaptobenzoic acid and 4-mercaptobutyric acid. Almost all of theabove bridging compounds are available commercially from Aldrich andother chemical suppliers.

When a symmetrical charge transport material of Formula (I) is desired,the arylamine hydrazone compound having Formula (IIA) should be the sameas the arylamine hydrazone compound having Formula (IIB) and thebridging compound is symmetrical. In the other words, a symmetricalcharge transport material may be obtained when Y₁ and Y₂ are the same,R₁ and R₂ are the same, R₃ and R₄ are the same, X and X′ are the same,E₁ and E₂ are the same, Q₁ and Q₂ are the same, and X₃ is symmetrical.To prepare a symmetrical charge transport material of Formula (I), asymmetrical bridging compound may react with an arylamine hydrazonecompound having Formula (II) in a molar ratio of at least 1:2.Optionally, an excess of the arylamine hydrazone compound may be used tomaximize the desirable symmetrical charge transport material of Formula(I).

When an unsymmetrical charge transport material of Formula (I) isdesired, the arylamine hydrazone compound having Formula (IIA) should bedifferent from the arylamine hydrazone compound having Formula (IIB) orthe bridging compound is unsymmetrical. In the other words, anunsymmetrical charge transport material may be obtained when Y₁ and Y₂are different, R₁ and R₂ are different, R₃ and R₄ are different, X andX′ are different, E₁ and E₂ are different, Q₁ and Q₂ are different, orX₃ is unsymmetrical. To prepare an unsymmetrical charge transportmaterial of Formula (I), a bridging compound may react with twodifferent arylamine hydrazone compounds in two sequential reactions. Inthe first reaction, the bridging compound may react with a firstarylamine hydrazone compound. Optionally, an excess of the bridgingcompound may be used to maximize the desirable product and to minimizethe undesirable symmetrical side product. In the second reaction, theproduct obtained in the first reaction may react with a second arylaminehydrazone compound to form the desirable unsymmetrical charge transportmaterial of Formula (I).

The desired product, either symmetrical or unsymmetrical, may beisolated and purified by the convention purification techniques such ascolumn chromatography, thin layer chromatography, and recrystallization.

The ring-opening reaction between the —X-E₁ group and the -Q₁H group (orthe -Q₂H group) produces the —X₁-Q₁- group (or the —X₁-Q₂- group); andthe ring-opening reaction between the —X′-E₂ group and the -Q₂H group(or the -Q₁H group) produces the —X₂-Q₂- group (or the —X₂-Q₁- group).X₁ and X₂ may be the same or different. X₁ and X₂ are the same when Xand X′ are the same, E₁ and E₂ are the same, Q₁ and Q₂ are the same, andX₃ is symmetrical. X₁ and X₂ are different when X and X′ are different,E₁ and E₂ are different, Q₁ and Q₂ are different, or X₃ is unsymmetrical

Although ring-opening reactions between reactive ring groups andfunctional groups that are reactive toward the reactive ring groups aredisclosed here, other suitable synthetic reactions between two differentfunctional groups that are reactive toward each other may be utilizedfor the co-polymerization in the fourth step. For example, Q₁ and Q₂ maybe, each independently, hydroxyl or amine groups (or, eachindependently, carboxylic acid or halide groups) and E₁ and E₂ may be,each independently, carboxylic acid or halide groups (or, eachindependently, hydroxyl or amine groups) that react with the hydroxyl oramine groups (or carboxylic acid or halide groups) to produce a chargetransport material of Formula (I) where X₁ and X₂ comprise, eachindependently, an ester or amide group respectively, or a combinationthereof. Another example is that Q₁ and Q₂ may be amino groups (orcarbonyl groups) and E₁ and E₂ may be carbonyl groups (or amino groups)that react with the amino groups (or carbonyl groups) to produce acharge transport material of Formula (I) where X₁ and X₂ comprise, eachindependently, an imine group. A further example is that Q₁ and Q₂ maybe isocyanate groups (or, each independently, hydroxyl, thiol, or aminegroups) and E₁ and E₂ may be, each independently, hydroxyl, thiol, oramine groups (or isocyanate groups) that react with the isocyanategroups (or hydroxyl, thiol, or amine groups) to produce a chargetransport material of Formula (I) where X₁ and X₂ comprise, eachindependently, a urethane, thiocarbamate, or urea group respectively, ora combination thereof. An additional example is that the E₁ group inFormula (IIA) may be exchanged with the Q₁ group in the bridgingcompound; or both the E₁ and E₂ groups in Formula (IIA) and Formula(IIA) respectively may be exchanged with the Q₁ and Q₂ groups in thebridging compound.

Alternatively, the charge transport materials of Formula (I) may beprepared by coupling two arylamine hydrazones having a thiol group. Thecoupling reaction may be carried out by heating the arylamine hydrazoneshaving a thiol group in dimethyl sulfoxide (DMSO). The two arylaminehydrazones may be the same or different. The product can be purified bycolumn chromatography and/or recrystallization. The two arylaminehydrazones having a thiol group may be prepared by reacting thecorresponding arylamine hydrazones having a reactive ring group with anon-aromatic dithiol, such 3,6-dioxa-1,8-octanedithiol,erythro-1,4-dimercapto-2,3-butanediol,(±)-threo-1,4-dimercapto-2,3-butanediol, 1,2-ethanedithiol,1,3-propanedithiol, 1,4-butanedithiol, 2,3-butanedithiol,1,5-pentanedithiol, and 1,6-hexanedithiol. The above and many othersnon-aromatic dithiols are available commercially from Aldrich and otherchemical suppliers. The reaction may be catalyzed by a base, such astriethylamine. Other suitable reactions for preparing the chargetransport materials of Formula (I) can be used by a person of ordinaryskill in the art based on the disclosure herein.

The invention will now be described further by way of the followingexamples.

EXAMPLES Example 1 Synthesis and Characterization Charge TransportMaterials

This example describes the synthesis and characterization of Compounds(1)–(5) and Diastereomers (2a) and (2b) in which the numbers refer toformula numbers above. The characterization involves chemicalcharacterization of the compounds. The electrostatic characterization,such as mobility and ionization potential, of the materials formed withthe compounds is presented in a subsequent example.

Preparation of 4-(Diphenylamino)benzaldehydeN-2,3-Epoxypropyl-N-Phenylhydrazone

Phenylhydrazine (0.1 mole, from Aldrich, Milwaukee, Wis.) and4-(diphenylamino)benzaldehyde (0.1 mole, from Fluka, Buchs SG,Switzerland) were dissolved in 100 ml of isopropanol in a 250 ml 3-neckround bottom flask equipped with a reflux condenser and a mechanicalstirrer. The solution was refluxed for 2 hours. At the end of thereaction, as indicated by thin layer chromatography the disappearance ofthe starting materials, the mixture was cooled to room temperature. The4-(diphenylamino)benzaldehyde phenylhydrazone crystals that formed uponstanding were filtered off, washed with isopropanol, and dried in avacuum oven at 50° C. for 6 hours.

A mixture of 4-(diphenylamino)benzaldehyde phenylhydrazone (3.6 g, 0.01mole), 85% powdered potassium hydroxide (2.0 g, 0.03 mole) and anhydrouspotassium carbonate (0.69 g, 0.005 mole) in epichlorohydrin (25 ml) wasstirred vigorously at 55–60° C. for 1.5–2 hours. The course of thereaction was monitored by thin layer chromatography using silica gel 60F254 plates (from Merck, Whitehouse Station, N.J.) using a mixture ofacetone and hexane in a volume ratio of 1:4 as eluant. After thetermination of the reaction, the mixture was cooled to room temperature,diluted with ether, and washed with water until the washed water reacheda neutral pH. The organic phase was dried over anhydrous magnesiumsulfate, treated with activated charcoal, and filtered. Ether wasremoved from the organic phase and the residue was dissolved in amixture of toluene and isopropanol in a volume ratio of 1:1. Thecrystals formed upon standing were filtered off and washed withisopropanol to yield 3.0 g (71.4%) of the product,4-(diphenylamino)benzaldehyde N-2,3-epoxypropyl-N-phenylhydrazone. Theproduct was recrystallized from a mixture of toluene and isopropanol ina volume ratio of 1:1. The melting point of the recrystallized productwas found to be 141–142.5° C. The ¹H-NMR spectrum (250 MHz) of theproduct in CDCl₃ was characterized by the following chemical shifts (δ,ppm): 7.65–6.98 (m, 19H), 6.93 (t, J=7.2 Hz, 1H), 4.35 (dd, 1H), 3.99(dd, 1H), 3.26 (m, 1H), 2.84 (dd, 1H), and 2.62 (dd, 1H). An elementalanalysis yielded the following results in weight percent: C 80.02, H6.31, and N 9.91, which compares with calculated values for C₂₈H₂₅N₃O inweight percent: C 80.16, H 6.01, and N 10.02.

Compound (1)

A mixture of 4-(diphenylamino)benzaldehydeN-2,3-epoxypropyl-N-phenylhydrazone (6.0 g, 14.30 mmol),3,6-dioxa-1,8-octanedithiol (1.24 g, 6.81 mmol, obtained from Aldrich),2-butanone (10 ml), and triethylamine (0.8 ml, 5.74 mol) was added to a50 ml 3-neck round bottom flask equipped with a reflux condenser and amechanical stirrer. The mixture was refluxed for 4 hours. After thesolvent was evaporated, the residue was subjected to columnchromatography (silica gel, grade 62, 60–200 mesh, 150 Å, Aldrich) usinga mixture of acetone and hexane in a volume ratio of 1:4 as the eluant.Fractions containing the product were collected and the solvents wereevaporated to yield an oily residue. The oily residue was dissolved intoluene to form a 20% solution. The solution was poured with intensivestirring into a tenfold excess of n-hexane to yield 4.7 g (68%) ofCompound (1). The ¹H-NMR spectrum (250 MHz) of the product in CDCl₃ wascharacterized by the following chemical shifts (δ, ppm): 7.70 (s, 2H,CH═N); 7.55 (d, 4H, p-Ph); 7.43 (d, 4H, p-Ph); 7.37–6.99 (m, 28H, Ar);6.95 (m, 2H, 4-H of ═N—N-Ph); 4.27–4.12 (m, 2H, CH); 4.09–3.90 (m, 4H,NCH₂); 3.71–3.52 (m, 10H, CH₂OCH₂, OH); and 2.88–2.60 (m, 8H, CH₂SCH₂).An elemental analysis yielded the following results in weight percent:C, 72.69; H 6.15; and N 8.03, which compared with calculated values forC₆₂H₆₄N₆O₄S₂ in weight percent: C, 72.91; H 6.32; and N 8.23.

Compound (2)

A mixture of 4-(diphenylamino)benzaldehydeN-2,3-epoxypropyl-N-phenylhydrazone (6.0 g, 14.30 mmol),2,3-butanedithiol (0.83 g, 6.81 mmol, from Aldrich), 2-butanone (10 ml),and triethylamine (0.8 ml, 5.74 mol) was added to a 50 ml 3-neck roundbottom flask equipped with a reflux condenser and a mechanical stirrer.The mixture was refluxed for 6 hours. After the solvent was evaporated,the residue was subjected to column chromatography (silica gel, grade62, 60–200 mesh, 150 Å, Aldrich) using a mixture of acetone and hexanein a volume ratio of 1:4 as the eluant. Fractions containing the productwere collected and the solvents were evaporated to yield an oilyresidue. The oily residue was dissolved in toluene to form a 20%solution. The solution was poured with intensive stirring into a tenfoldexcess of n-hexane to yield 4.7 g (68%) of Compound (2) as a mixture ofdiastereomers (2a) and (2b). The ¹H-NMR spectrum (250 MHz) of theproduct in CDCl₃ was characterized by the following chemical shifts (δ,ppm): 7.66 (s, split, 2H, CH═N); 7.55 (d, 4H, p-Ph); 7.44–7.18 (m, 16H,Ar); 7.16–6.92 (m, 18H, Ar); 4.26–4.12 (m, 2H, CH); 4.07–3.92 (m, 4H,NCH₂); 3.29–3.56 (m, 8H, CH₂SCH, OH); and 1.37 (d, 6H, CH₃). Anelemental analysis yielded the following results in weight percent: C,74.68; H 6.05; and N 8.53, which compared with calculated values forC₆₀H₆₀N₆O₂S₂ in weight percent: C, 74.97; H 6.29; and N 8.74.

Diastereomer (2a) and (2b)

Diastereomers (2a) and (2b) were separated from the mixture obtainedabove by column chromatography with silica gel (grade 62, 60–200 mesh,150 Å, from Aldrich) using a mixture of acetone and hexane in a volumeratio of 1:4 as the eluant. Fractions containing Diastereomer (2a)(characterized by thin layer chromatography with a R_(f) value of 0.38using Silufol UV-254 and a mixture of acetone and hexane in a volumeratio of 1:2.6 as eluant) were collected and the solvents wereevaporated to yield an oily residue. The oily residue was dissolved intoluene to form a 20% solution. The solution was poured with intensivestirring into a tenfold excess of n-hexane to yield 0.8 g ofDiastereomer (2a). An elemental analysis yielded the following resultsin weight percent: C, 74.78; H 6.08; and N 8.56, which compared withcalculated values for C₆₀H₆₀N₆O₂S₂ in weight percent: C, 74.97; H 6.29;and N 8.74.

Fractions containing Diastereomer (2b) (characterized by thin layerchromatography with a R_(f) value of 0.31 using Silufol UV-254 and amixture of acetone and hexane in a volume ratio of 1:2.6 as eluant) werecollected and the solvents were evaporated to yield an oily residue. Theoily residue was dissolved in toluene to form a 20% solution. Thesolution was poured with intensive stirring into a tenfold excess ofn-hexane to yield 2 g of Diastereomer (2b). An elemental analysisyielded the following results in weight percent: C, 74.69; H 6.09; and N8.55, which compared with calculated values for C₆₀H₆₀N₆O₂S₂ in weightpercent: C, 74.97; H 6.29; and N 8.74.

Compound (3)

A mixture of 4-(diphenylamino)benzaldehydeN-2,3-epoxypropyl-N-phenylhydrazone (6.0 g, 14.30 mmol) anderythro-1,4-dimercapto-2,3-butanediol (1.05 g, 6.81 mmol, from Aldrich),2-butanone (10 ml), and triethylamine (0.8 ml, 5.74 mol) was added to a50 ml 3-neck round bottom flask equipped with a reflux condenser and amechanical stirrer. The mixture was refluxed for 2 hours. After theevaporation of the solvent, the residue was subjected to columnchromatography (silica gel, grade 62, 60–200 mesh, 150 Å, Aldrich) usinga mixture of acetone and hexane in a volume ratio of 1:4 as the eluant.Fractions containing the product were collected and the solvents wereevaporated to yield a residue. The residue was recrystallized fromtoluene to yield 4.3 g (64%) of Compound (3). The melting point ofCompound (3) was found to be 166–167.5° C. The ¹H-NMR spectrum (300 MHz)of the product in DMSO-d₆ was characterized by the following chemicalshifts (δ, ppm): 7.85 (s, 2H, CH═N); 7.59 (d, 4H, p-Ph); 7.45 (d, 4H,p-Ph); 7.36–7.16 (m, 12H, Ar); 7.12–6.90 (m, 16H, Ar); 6.82 (t, 2H, 4-Hof ═N—N-Ph); 5.31 (s, br, 2H, OH); 5.0 (m, 2H, OH); 4.15–3.85 (m, 6H,NCH₂CH); and 3.62–2.51 (m, 6H, CH₂SCHCHSCH₂). An elemental analysisyielded the following results in weight percent: C 72.37; H 5.92; and N8.30, which compared with calculated values for C₆₀H₆₀N₆O₄S₂. in weightpercent: 72.55; H 6.09; and N 8.46

Compound (4)

6.0 g (14.30 mmol) of4-(diphenylamino)benzaldehyde-N-2,3-epoxypropyl-N-phenylhydrazone and1.05 g (6.81 mmol) of (±)-threo-1,4-dimercapto-2,3-butanediol (obtainedfrom Aldrich) were dissolved in 10 ml of 2-butanone and 0.8 ml (5.74mol) of TEA were added. The mixture was refluxed for 2 hours. After theevaporation of the solvent, the residue was subjected to columnchromatography (silica gel, grade 62, 60–200 mesh, 150 Å, Aldrich) usinga mixture of acetone and hexane in a volume ratio of 1:4 as the eluent.Fractions containing the product were collected and the solvents wereevaporated to yield an oily residue. The oily residue was dissolved intoluene to form a 20% solution. The solution was poured with intensivestirring into a tenfold excess of n-hexane to yield 4.8 g (71%) ofCompound (4). The ¹H-NMR spectrum (300 MHz) of the product in DMSO-d₆was characterized by the following chemical shifts (δ, ppm): 7.85 (m,2H, CH═N); 7.58 (m, 4H, p-Ph); 7.45 (m, 4H, p-Ph); 7.35–7.18 (m, 12H,Ar); 7.12–6.92 (m, 16H, Ar); 6.82 (m, 2H, 4-H of ═N—N-Ph); 5.32 (s, br,2H, OH); 4.82 (m, 2H, OH); 4.14–3.86 (m, 6H, NCH₂CH); 3.74–3.51 (m, 6H,CH₂SCHCHSCH₂). An elemental analysis yielded the following results inweight percent: C 72.39; H 5.90; N 8.28 which compared with calculatedvalues for C₆₀H₆₀N₆O₄S₂ in weight percent of: C 72.55; H 6.09; N 8.46.

Compound (5)

4-(Diphenylamino)benzaldehydeN-[2-Hydroxy-3-(2-thiol-ethylsulfanyl)-propyl]-N-phenyl hydrazone

A mixture of 4-(diphenylamino)benzaldehyde N-2,3-epoxypropyl-N-phenylhydrazone (5.0 g, 11.92 mmol) in 10 ml butanone (commercially obtainedfrom Aldrich, Milwaukee, Wis.), 1,2-ethanedithiol (1.12 g (1.0 ml),11.92 mmol, obtained from Fluka) and triethylamine (0.48 g (0.66 ml),4.77 mmol) was added to a 50 ml 3-neck round bottom flask equipped witha reflux condenser and a mechanical stirrer. The mixture was refluxedovernight. The product was purified by chromatography using a columnpacked with silica gel (grade 62, 60–200 mesh, 150 Å, commerciallyobtained from Aldrich, Milwaukee, Wis.) and an eluant mixture of hexaneand acetone in a 7:1 ratio by volume. Fractions containing theintermediate, 4-(diphenylamino)benzaldehydeN-[2-hydroxy-3-(2-thiol-ethylsulfanyl)-propyl]-N-phenyl hydrazone, werecollected and the intermediate was recrystallized from eluant to yield2.45 g (40%). The melting point of the intermediate was found to be117–119° C. The infrared spectrum of the intermediate was characterizedby the following absorption peaks (KBr window, cm⁻¹): 3600–3200 (OH,broad); 3061, 3033 (aromatic CH); 2952, 2916 (aliphatic CH); 2539 (SH);and 646, 622, 616 (C—S). The ¹H-NMR spectrum (100 MHz) of the product inCDCl₃ was characterized by the following chemical shifts (δ, ppm): 7.638(s, 1H, CH═N); δ 7.50–6.90 (m, 19H, Ar); 4.30–3.90 (m, 2H, NCH₂); 3.02(d, 1H, J=3.0 Hz, OH); 2.97–2.50 (m, 6H, CH₂SCH₂, CH ₂SH); and 1.80–1.55(m, 1H, SH). An elemental analysis yielded the following results inweight percent: C, 69.98; H 5.83; N 8.67, which compared with calculatedvalues for C₃₀H₃₁N₃OS₂ in weight percent of: C, 70.14; H 6.08; N 8.18.

The intermediate obtained above (1.3 g, 2.53 mmol,) was dissolved in 5ml dimethyl sulfoxide (DMSO) (obtained from Aldrich, A. C. S. reagent).After the solution was stirred at 85–90° C. over night, the hot solutionwas poured into the water. The resulting solid was filtered off andwashed with water to remove DMSO and then with 2-proponol. The crudeproduct was purified by chromatography using a column packed with silicagel (grade 62, 60–200 mesh, 150 Å, from Aldrich, Milwaukee, Wis.) and aneluant mixture of hexane and acetone in a 7:1 ratio by volume. Fractionscontaining the product were collected and the eluant was evaporated toyield an oily residue. A 20% solution of the oily residue in toluene wasprepared and then poured with intensive stirring into a tenfold excessof hexane to yield 1.54 g (59.5%) of Compound (5) as a yellowish powder.The infrared spectrum of the intermediate was characterized by thefollowing absorption peaks (KBr window, cm⁻¹): 3433 (OH, broad); 3059,3034 (aromatic CH); 2910 (aliphatic CH); 827 (CH═CH of 1,4-disubstitutedbenzene); 752, 695 (CH═CH of monosubstituted benzene); and 645, 622, 617(C—S). The ¹H-NMR spectrum (300 MHz) of the product in DMSO-d₆ wascharacterized by the following chemical shifts (δ, ppm): 7.84 (s, 2H,CH═N); 7.58 (d, 4H, Ar); 7.44 (d, 4H, Ar); 7.37–7.28 (m, 12H, Ar);7.15–6.91 (m, 16H, Ar); 6.83 (t, 2H, 4-H of C₆H₅NN); 5.35 (d, 2H, J=4.8Hz, OH); 4.12 0–3.90 (m, 6H, NCH₂CH); 3.03–2.82 (m, 8H, CH₂SCH₂); and2.82–2.63 (m, 4H, CH₂SSCH₂). An elemental analysis yielded the followingresults in weight percent: C, 70.65; H 5.86; N 8.45, which compared withcalculated values for C₆₀H₆₀N₆O₂S₄: in weight percent of: C, 70.28; H5.90; N 8.20.

Example 2 Charge Mobility Measurements

This example describes the measurement of charge mobility and ionizationpotential for charge transport materials, specifically Compounds (1),(3)-(5), and Diastereomers (2a) and (2b) above.

Sample 1

A mixture of 0.1 g of Compound (1) and 0.1 g of polyvinylbutyral (S-LECB BX-1, commercially obtained from Sekisui) was dissolved in 2 ml oftetrahydrofuran (THF). The solution was coated on a polyester film witha conductive aluminum layer by a dip roller. After the coating was driedfor 1 hour at 80° C., a clear 10 μm thick layer was formed. The holemobility of the sample was measured and the results are presented inTable 1.

Sample 2

Sample 2 was prepared according to the procedure for Sample 1 exceptthat Diastereomer (2a) replaced Compound (1).

Sample 3

Sample 3 was prepared according to the procedure for Sample 1 exceptthat Diastereomer (2b) replaced Compound (1).

Sample 4

Sample 4 was prepared according to the procedure for Sample 1 exceptthat Compound (3) replaced Compound (1).

Sample 5

Sample 5 was prepared according to the procedure for Sample 4 exceptthat no binder was used.

Sample 6

Sample 6 was prepared according to the procedure for Sample 1 exceptthat Compound (4) replaced Compound (1).

Sample 7

Sample 7 was prepared according to the procedure for Sample 6 exceptthat no binder was used.

Sample 8

Sample 8 was prepared according to the procedure for Sample 1 exceptthat Compound (5) replaced Compound (1).

Mobility Measurements

Each sample was corona charged positively up to a surface potential Uand illuminated with 2 ns long nitrogen laser light pulse. The holemobility μ was determined as described in Kalade et al., “Investigationof charge carrier transfer in electrophotographic layers of chalkogenideglasses,” Proceeding IPCS 1994: The Physics and Chemistry of ImagingSystems, Rochester, N.Y., pp. 747–752, incorporated herein by reference.The hole mobility measurement was repeated with appropriate changes tothe charging regime to charge the sample to different U values, whichcorresponded to different electric field strength inside the layer E.This dependence on electric field strength was approximated by theformulaμ=μ₀ e ^(α√{square root over (E)}).Here E is electric field strength, μ₀ is the zero field mobility and αis Pool-Frenkel parameter. Table 1 lists the mobility characterizingparameters μ₀ and α values and the mobility value at the 6.4×10⁵ V/cmfield strength as determined by these measurements for the four samples.

TABLE 1 μ (cm²/V · s) Ionization Sample μ₀ (cm²/V · s) at 6.4 · 10⁵ V/cmα (cm/V)^(0.5) Potential (eV) Compound (1) / / / 5.42 Diastereomer (2a)/ / / 5.42 Diastereomer (2b) / / / 5.42 Compound (3) / / / 5.44 Compound(4) / / / 5.40 Compound (5) / / / 5.38 Sample 1 3.6 × 10⁻⁸ 1.0 × 10⁻⁶0.0034 / Sample 2 4.0 × 10⁻⁸ 2.3 × 10⁻⁶ 0.0050 / Sample 3 2.7 × 10⁻⁸ 2.0× 10⁻⁶ 0.0054 / Sample 4 1.6 × 10⁻⁸ 1.4 × 10⁻⁶ 0.0056 / Sample 5 1.2 ×10⁻⁶ 7.0 × 10⁻⁵ 0.0050 / Sample 6 1.2 × 10⁻⁸ 1.3 × 10⁻⁶ 0.0058 / Sample7 ~2.0 × 10⁻⁶   1.0 × 10⁻⁴ ~0.0052 / Sample 8 1.9 × 10⁻⁸ 7.6 × 10⁻⁷0.0046 /

Example 3 Ionization Potential Measurements

This example describes the measurement of the ionization potential forthe 5 charge transport materials described in Example 1.

To perform the ionization potential measurements, a thin layer of chargetransport material about 0.5 μm thickness was coated from a solution of2 mg of charge transport material in 0.2 ml of tetrahydrofuran on a 20cm² substrate surface. The substrate was an aluminized polyester filmcoated with a 0.4 μm thick methylcellulose sub-layer.

Ionization potential was measured as described in Grigalevicius et al.,“3,6-Di(N-diphenylamino)-9-phenylcarbazole and its methyl-substitutedderivative as novel hole-transporting amorphous molecular materials,”Synthetic Metals 128 (2002), p. 127–131, incorporated herein byreference. In particular, each sample was illuminated with monochromaticlight from the quartz monochromator with a deuterium lamp source. Thepower of the incident light beam was 2–5·10⁻⁸ W. A negative voltage of−300 V was supplied to the sample substrate. A counter-electrode withthe 4.5×15 mm² slit for illumination was placed at 8 mm distance fromthe sample surface. The counter-electrode was connected to the input ofa BK2-16 type electrometer, working in the open input regime, for thephotocurrent measurement. A 10⁻¹⁵–10⁻¹² amp photocurrent was flowing inthe circuit under illumination. The photocurrent, I, was stronglydependent on the incident light photon energy hν. The I^(0.5)=f(hν)dependence was plotted. Usually, the dependence of the square root ofphotocurrent on incident light quanta energy is well described by linearrelationship near the threshold (see references “Ionization Potential ofOrganic Pigment Film by Atmospheric Photoelectron Emission Analysis,”Electrophotography, 28, Nr. 4, p. 364 (1989) by E. Miyamoto, Y.Yamaguchi, and M. Yokoyama; and “Photoemission in Solids,” Topics inApplied Physics, 26, 1–103 (1978) by M. Cordona and L. Ley, both ofwhich are incorporated herein by reference). The linear part of thisdependence was extrapolated to the hν axis, and the Ip value wasdetermined as the photon energy at the interception point. Theionization potential measurement has an error of ±0.03 eV. Theionization potential values are given in Table 1 above.

As understood by those skilled in the art, additional substitution,variation among substituents, and alternative methods of synthesis anduse may be practiced within the scope and intent of the presentdisclosure of the invention. The embodiments above are intended to beillustrative and not limiting. Additional embodiments are within theclaims. Although the present invention has been described with referenceto particular embodiments, workers skilled in the art will recognizethat changes may be made in form and detail without departing from thespirit and scope of the invention.

1. An organophotoreceptor comprising an electrically conductive substrate and a photoconductive element on the electrically conductive substrate, the photoconductive element comprising: (a) charge transport material having the formula

 where R₁ and R₂ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; R₃ and R₄ are, each independently, H, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; X₁ and X₂ are, each independently, a linking group; Y₁ and Y₂, each independently, comprise an arylamine group; and Z is a bridging group having the formula -Q₁-X₃-Q₂- where Q₁ and Q₂ comprise, each independently, O, S, or NR where R is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group; and X₃ comprises a —(CH₂)_(p)— group where p is an integer between 1 and 20, inclusive, and at least one of the methylene groups is replaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h) group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i), R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group; and (b) a charge generating compound.
 2. An organophotoreceptor according to claim 1 wherein Y₁ and Y₂, each independently, comprise a carbazole group, a julolidine group, or an (N,N-disubstituted)arylamine group.
 3. An organophotoreceptor according to claim 1 wherein X₁ and X₂ are, each independently, a —(CH₂)_(m)— group, where m is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NR_(a) group, a CR_(b) group, a CR_(c)R_(d) group, or a SiR_(e)R_(f) where R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group.
 4. An organophotoreceptor according to claim 3 wherein X₁ and X₂ are, each independently, a —CH₂—CH(Q₃H)—CH₂— group where Q₃ is O, S, or NR′where R′ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group.
 5. An organophotoreceptor according to claim 1 wherein X₃ is a —CH₂—CH(Q₄H)—CH(Q₅H)—CH₂— group, a —CH(R₅)—CH(R₆)— group, or a —CH₂—CH₂-Q₆-CH₂—CH₂-Q₇-CH₂—CH₂— group where R₅ and R₆ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group; and Q₄, Q₅, Q₆, and Q₇, are, each independently, O, S, or NR″ where R″ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group.
 6. An organophotoreceptor according to claim 1 wherein the photoconductive element further comprises a second charge transport material.
 7. An organophotoreceptor according to claim 6 wherein the second charge transport material comprises an electron transport compound.
 8. An organophotoreceptor according to claim 1 wherein the photoconductive element further comprises a binder.
 9. An electrophotographic imaging apparatus comprising: (a) a light imaging component; and (b) an organophotoreceptor oriented to receive light from the light imaging component, the organophotoreceptor comprising an electrically conductive substrate and a photoconductive element on the electrically conductive substrate, the photoconductive element comprising: (i) a charge transport material having the formula

where R₁ and R₂ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; R₃ and R₄ are, each independently, H, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; X₁ and X₂ are, each independently, a linking group; Y₁ and Y₂, each independently, comprise an arylamine group; and Z is a bridging group having the formula -Q₁-X₃-Q₂- where Q₁ and Q₂ comprise, each independently, O, S, or NR where R is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group; and X₃ comprises a —(CH₂)_(p)— group where p is an integer between 1 and 20, inclusive, and at least one of the methylene groups is replaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h) group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i), R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group; and (ii) a charge generating compound.
 10. An electrophotographic imaging apparatus according to claim 9 wherein Y₁ and Y₂, each independently, comprise a carbazole group, a julolidine group, or an (N,N-disubstituted)arylamine group.
 11. An electrophotographic imaging apparatus according to claim 9 wherein X₁ and X₂ are, each independently, a —(CH₂)_(m)— group, where m is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NR_(a) group, a CR_(b) group, a CR_(c)R_(d) group, or a SiR_(e)R_(f) where R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group.
 12. An electrophotographic imaging apparatus according to claim 11 wherein X₁ and X₂ are, each independently, a —CH₂—CH(Q₃H)—CH₂— group where Q₃ is O, S, or NR′where R′ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group.
 13. An electrophotographic imaging apparatus according to claim 9 wherein X₃ is a —CH₂—CH(Q₄H)—CH(Q₅H)—CH₂— group, a —CH(R₅)—CH(R₆)— group, or a —CH₂—CH₂-Q₆-CH₂—CH₂-Q₇-CH₂—CH₂— group where R₅ and R₆ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group; and Q₄, Q₅, Q₆, and Q₇, are, each independently, O, S, or NR″ where R″ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group.
 14. An electrophotographic imaging apparatus according to claim 9 wherein the photoconductive element further comprises a second charge transport material.
 15. An electrophotographic imaging apparatus according to claim 14 wherein second charge transport material comprises an electron transport compound.
 16. An electrophotographic imaging apparatus according to claim 9 further comprising a toner dispenser.
 17. An electrophotographic imaging process comprising; (a) applying an electrical charge to a surface of an organophotoreceptor comprising an electrically conductive substrate and a photoconductive element on the electrically conductive substrate, the photoconductive element comprising (i) a charge transport material having the formula

where R₁ and R₂ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; R₃ and R₄ are, each independently, H, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; X₁ and X₂ are, each independently, a linking group; Y₁ and Y₂, each independently, comprise an arylamine group; and Z is a bridging group having the formula -Q₁-X₃-Q₂- where Q₁ and Q₂ comprise, each independently, O, S, or NR where R is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group; and X₃ comprises a —(CH₂)_(p)— group where p is an integer between 1 and 20, inclusive, and at least one of the methylene groups is replaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h) group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i), R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group; and ii) a charge generating compound. (b) imagewise exposing the surface of the organophotoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of charged and uncharged areas on the surface; (c) contacting the surface with a toner to create a toned image; and (d) transferring the toned image to substrate.
 18. An electrophotographic imaging process according to claim 17 wherein Y₁ and Y₂, each independently, comprise a carbazole group, a julolidine group, or an (N,N-disubstituted)arylamine group.
 19. An electrophotographic imaging process according to claim 17 wherein X₁ and X₂ are, each independently, a —(CH₂)_(m)— group, where m is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NR_(a) group, a CR_(b) group, a CR_(c)R_(d) group, or a SiR_(e)R_(f) where R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group.
 20. An electrophotographic imaging process according to claim 19 wherein X₁ and X₂ are, each independently, a —CH₂—CH(Q₃H)—CH₂— group where Q₃ is O, S, or NR′where R′ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group.
 21. An electrophotographic imaging process according to claim 17 wherein X₃ is a —CH₂—CH(Q₄H)—CH(Q₅H)—CH₂— group, a —CH(R₅)—CH(R₆)— group, or a —CH₂—CH₂-Q₆-CH₂—CH₂-Q₇-CH₂—CH₂— group where R₅ and R₆ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group; and Q₄, Q₅, Q₆, and Q₇, are, each independently, O, S, or NR″ where R″ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group.
 22. An electrophotographic imaging process according to claim 17 wherein the photoconductive element further comprises a second charge transport material.
 23. An electrophotographic imaging process according to claim 22 wherein the second charge transport material comprises an electron transport compound.
 24. An electrophotographic imaging process according to claim 17 wherein the photoconductive element further comprises a binder.
 25. An electrophotographic imaging process according to claim 17 wherein the toner comprises colorant particles.
 26. A charge transport material having the formula

where R₁ and R₂ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; R₃ and R₄ are, each independently, H, an alkyl group, an alkenyl group, an alkynyl group, an aromatic group, or a heterocyclic group; X₁ and X₂ are, each independently, a linking group; Y₁ and Y₂, each independently, comprise an arylamine group; and Z is a bridging group having the formula -Q₁-X₃-Q₂- where Q₁ and Q₂ comprise, each independently, O, S, or NR where R is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group; and X₃ comprises a —(CH₂)_(p)— group where p is an integer between 1 and 20, inclusive, and at least one of the methylene groups is replaced by O, S, N, C, B, Si, P, C═O, O═S═O, an NR_(g) group, a CR_(h) group, a CR_(i)R_(j) group, or a SiR_(k)R_(l) where R_(g), R_(h), R_(i), R_(j), R_(k), and R_(l) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group.
 27. A charge transport material according to claim 26 wherein Y₁ and Y₂, each independently, comprise a carbazole group, a julolidine group, or an (N,N-disubstituted)arylamine group.
 28. A charge transport material according to claim 26 wherein X₁ and X₂ are, each independently, a —(CH₂)_(m)— group, where m is an integer between 1 and 20, inclusive, and one or more of the methylene groups is optionally replaced by O, S, N, C, B, Si, P, C═O, O═S═O, a heterocyclic group, an aromatic group, an NR_(a) group, a CR_(b) group, a CR_(c)R_(d) group, or a SiR_(e)R_(f) where R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) are, each independently, a bond, H, a hydroxyl group, a thiol group, a carboxyl group, an amino group, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group.
 29. A charge transport material according to claim 28 wherein X₁ and X₂ are, each independently, a —CH₂—CH(Q₃H)—CH₂— group where Q₃ is O, S, or NR′where R′ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group.
 30. A charge transport material according to claim 26 wherein X₃ is a —CH₂—CH(Q₄H)—CH(Q₅H)—CH₂— group, a —CH(R₅)—CH(R₆)— group, or a —CH₂—CH₂-Q₆-CH₂—CH₂-Q₇-CH₂—CH₂— group where R₅ and R₆ are, each independently, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, an aromatic group, or a part of a ring group; and Q₄, Q₅, Q₆, and Q₇, are, each independently, O, S, or NR″ where R″ is H, an alkyl group, an alkenyl group, an alkynyl group, a heterocyclic group, or an aromatic group. 